Medium voltage systems are often used to power heavy machinery, such as multiple high horsepower (e.g., 6000 hp) motors in a water pumping station. FIG. 1 illustrates an example system having two such motors 101a,b. Each motor 101a,b may be driven by electrical current supplied from a power supply line 102, and through corresponding fused medium voltage bypass controllers 103a,b. The bypass controllers 103a,b may include a switch, a fuse that may be rated to carry large amounts of current, such as 400 Amps, a contactor and a current sensor.
The individual bypass controllers 103a,b may connect the motors 101a,b to the supply line 102 to allow the motors 101a,b to be run “across the line,” or directly using the currents and phases of the supply line 102. However, during a startup procedure, it may be desirable to control one of the motors at less than normal frequency and thus operate the motor at some reduced speed because of load (e.g. pump) requirements.
Accordingly, during startup, the bypass controllers 103a,b are taken out of the control lines for the motors 101a,b. Instead, variable frequency drive 104 may be connected, via a non-fused medium voltage transfer controller 105a, to the idle motor 101a. The variable frequency drive 104 may gradually vary the voltage and frequency supplied to the motor 101a through the non-fused transfer controller 105a, to gradually bring motor 101a up to speed.
Depending on load requirements, the individual motors 101a,b may be brought up to speed sequentially, so that a first motor 101a is brought up to speed before a second one 101b. In such a case, the transfer controllers 105a,b are also sequentially added to the control lines (e.g., controller 105a is used during startup of motor 101a, controller 105b is used during startup of motor 101b, etc.).
The commercially-available bypass controllers 103a,b that are rated for large levels of current (e.g., greater than 400 amps) are only offered for sale in single, standalone cabinets, as depicted in FIG. 1. The individual cabinets house just the components needed for the controller 103a,b, and do not offer additional space for additional controllers. As a result, significant amounts of floor space are required to support the various individual cabinets shown in FIG. 1. Even more space is occupied with the cabling, such as supply line 102, output bus 106, and lines 107a,b to the motors 101a,b. 